1. Field of the Invention
The present invention relates to a screen, a display device using the screen, and a method of forming the screen and, more particularly, to a back projection type screen, a method of forming the back projection type screen, and back projection type image display device using the back projection type screen.
2. Related Background Art
There is available a conventional back type projection image display device having a schematic arrangement shown in FIG. 1. This arrangement employs an oblique incident type in which an incident angle .theta..sub.0 of image light of a central portion is not 0.degree.. There is also known a back projection type image display device of a vertical incident type in which the incident angle .theta..sub.0 is 0.degree..
Referring to FIG. 1, a projection lens 2 enlarges and projects image light from a CRT 3 onto a screen 1 through mirrors 4a and 4b. The projection lens 2, the CRT 3, and the mirrors 4a and 4b are housed in a cabinet 5.
In the image display device having the above arrangement, the screen 1 comprises a Fresnel lens sheet having a focusing function, a diffusion board mixed with a diffusion agent, or vertical lenticular lens sheet (lenticular lenses vertically extend) for controlling the viewing characteristics in the right-and-left direction of the screen.
When the incident angle .theta..sub.0 is not zero, i.e., when light is obliquely incident, it has been known that a Fresnel lens is manufactured such that the concentric center of a concentric prism portion formed on a sheet is located outside the sheet (this Fresnel lens is referred to as an eccentric Fresnel lens hereinafter).
In order to manufacture this prior eccentric Fresnel lens, one specific mold for the eccentric Fresnel lens must be usually prepared and manufactured in e.g., compression forming. It is difficult to manufacture different eccentric Fresnel lens molds asymmetrical in the eccentric direction due to their eccentricity as compared with the manufacture of a concentric mold.